Android SQlite，如何检查数据库中的值是否已经存在？

Question

public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub
        db.execSQL("CREATE TABLE " + DATABASE_TABLE_COURSES + " ("
                + KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, "
                + KEY_COURSE_ID + " TEXT NOT NULL, "
                + KEY_COURSE_TITLE + " TEXT NOT NULL, "
                + KEY_COURSE_CNUMBER + " TEXT NOT NULL, "
                + KEY_COURSE_SUBJECT + " TEXT NOT NULL, " 
                + KEY_COURSE_DAYS + " TEXT NOT NULL, "
                + KEY_COURSE_START_TIME + " TEXT NOT NULL, "
                + KEY_COURSE_END_TIME + " TEXT NOT NULL, "
                + KEY_COURSE_PROFESSOR + " TEXT NOT NULL, "
                + KEY_COURSE_BUILDING + " TEXT NOT NULL, " 
                + KEY_COURSE_ROOM_NUMBER + " TEXT NOT NULL);");

I want to check that if the course_id already exists in the table, then don't make another entry. Thanks

Answer 1

To check if a field exists or not in general :

 Cursor cur1=db.query("database_table_courses", "course_id=id_u_wanttocheck", null, null, null, null, null);
      cur1.moveToLast();
      int count1=cur1.getCount();
      if(count1==0)
      {
          //course id not present

      }
      else
      {
        //course id present
      }

Or if you want the course_id to be never repeated in the table, you can set that as the primary key and remove the primary key tag from row_no . This way you can simply insert a new row. If the course_id is alreday present it willnot insert and throw an exception - SQLException , you can catch it and do what ever you want.